Piston-driven drug pump devices

ABSTRACT

In piston-pump drug-delivery devices, changes in friction between the piston and vial in which it moves may be reduced and/or compensated for by suitable surface coatings and/or feedback control.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of, and incorporatesherein by reference in its entirety, U.S. Provisional PatentApplications No. 61/326,047, filed on Apr. 20, 2010, No. 61/367,686,filed on Jul. 26, 2010, No. 61/423,945, filed on Dec. 16, 2010, and No.61/449,899, filed on Mar. 7, 2011.

TECHNICAL FIELD

The invention relates, generally, to drug pump devices, and, in variousembodiments, to electrolysis-driven piston pump devices.

BACKGROUND

As patients live longer and are diagnosed with chronic and oftendebilitating ailments, there is an increased need for improvements tothe speed, convenience, and efficacy of drug delivery. For example, manychronic conditions, including multiple sclerosis, diabetes,osteoporosis, and Alzheimer's disease, are incurable and difficult totreat with currently available therapies: oral medications have systemicside effects; injections may require a medical visit, can be painful,and risk infection; and sustained-release implants must typically beremoved after their supply is exhausted, and offer limited ability tochange the dose in response to the clinical picture. In recent decades,several types of wearable drug delivery devices have been developed,including battery-powered miniature pumps, implantable drug dispensers,and diffusion-mediated skin patches.

Treatments for a number of chronic diseases currently requiresubcutaneous administration of a drug or therapeutic agent eithercontinuously or at specific times or time intervals in highly controlleddoses. Subcutaneous injections take advantage of the lack of blood flowto the subcutaneous layer, which allows the administered drug to beabsorbed more slowly over a longer period of time (compared with directinjection into the blood stream). Additional advantages to subcutaneousdelivery of some drugs (i.e., vaccines, tuberculin tests,immunostimulants, etc.) to the tissue region are the targeting of lymphtissue and lymphatic drainage for subsequent antigen presentation to thebody. Traditionally, these types of injections have been administeredeither by the patient or a medical practitioner anywhere from severaltimes a day to once every few weeks. Such frequent injections can resultin discomfort, pain, and inconvenience to the patient.Self-administration further poses the risk of non-compliance or errorsin dosage events.

These problems can be at least partially overcome by wearable,electronically controlled drug pump devices that are, in principle,capable of delivering highly controlled dosages of drug continuously orintermittently, depending on the needs of the patient. Such devicesoften take the form of piston pump devices, in which pressure impartedon a piston causes the piston to move inside a drug-filled, elongated(e.g., cylindrical) reservoir, thereby pushing liquid drug out of thereservoir. The pressure can be generated, e.g., by an electrolysis pumpthat creates gaseous electrolysis products inside a pump chamberadjacent the piston, and can typically be controlled with high accuracyvia the electrical drive current supplied to the pump. The drug-deliveryrate, however, depends not only on the pump pressure, but also on thedegree of friction between the piston and the reservoir walls. Thisdegree of friction typically varies during drug-delivery, for example,as a consequence of the difference between static and dynamic friction,as well as due to changes of the surface properties of the piston andreservoir walls in time. As a result, the drug flow rate can changeabruptly and unpredictably despite uniform pump pressure, potentiallyhaving adverse health effects on the patient. Accordingly, there is aneed for devices that can reduce the effect of variations in friction.

SUMMARY

The present invention provides, in various embodiments, piston pumpdevices in which changes in friction between the piston and the walls ofthe drug reservoir are reduced or compensated for by suitable surfacecoatings, feedback control of the pump rate, or a combination of both.In certain embodiments, the drug reservoir is contained in a glass orpolymer drug vial, whose inner surface is coated to reduce thedifference between static and dynamic coefficients of friction. Suitablecoating materials include, for example, polytetrafluoroethylene andparylene. Further, some embodiments involve monitoring a parameterindicative of the drug-delivery rate (e.g., a flow rate, pressure at ornear the outlet of the drug reservoir, or piston position), andadjusting the pump pressure (in the case of an electrolysis pump via acurrent supplied to the electrolysis electrodes) based on the parameter.This feedback approach may facilitate compensating for variations infriction in (near) real-time.

Accordingly, in a first aspect, the invention provides a drug pumpdevice including a vial (e.g., made of glass or a polymer) that containsa drug reservoir therein, a piston movably disposed inside the vial andhaving first side facing the drug reservoir, and a pump for applyingpressure to a second side of the piston so as to move the piston tocause drug delivery from the reservoir. The device further includes oneor more sensors for measuring one or more parameters indicative of arate of drug delivery from the reservoir, and a controller responsive tothe sensor for adjusting the pressure so as to compensate for variationsin friction between the piston and an interior surface of the vial.

The controller may compensate for variations in friction due to adifference between a static coefficient of friction and a dynamiccoefficient of friction between the piston and the interior surface ofthe vial. The vial and/or the piston may include a surface coating thatreduces the difference between the static and dynamic coefficients offriction, e.g., by reducing the static coefficient of friction (whileleaving the dynamic coefficient substantially unchanged). The surfacecoating may include or essentially consist of polytetrafluoroethylene orparylene. The controller may also compensate for variations in frictiondue to a changing surface property of the piston and/or the vial.

In some embodiments, the vial is formed from a conventional drug vial.The pump may be an electrolysis pump, and the controller may adjusts thepressure by adjusting a rate of electrolysis. The device may furtherinclude a cannula conducting liquid from the drug reservoir, and thesensor(s) may be or include a flow sensor positioned in the cannula.Alternatively or additionally, the sensor may be or include a pressuresensor or a position sensor associated with the piston (such as, e.g., amagnet associated with the piston and an induction coil surrounding thevial). The device may include a pressure sensor and a flow sensor, andinputs of the pressure and flow sensors may facilitate recognizingmalfunctions in the device.

In another aspect, the invention is directed to a method, to be carriedout in a drug pump device including a drug reservoir and a piston, forcompensating for variations in friction that affect movement of thepiston. The piston is responsive to pressure and may force fluid out ofthe drug reservoir. The method includes measuring a parameter indicativeof a rate of drug delivery from the reservoir, and adjusting pressure onthe piston based on the measurement so as to compensate for thevariations in friction.

As used herein, the term “substantially” means ±10% and, in someembodiments, ±5%.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and the following detailed description of the inventionmay be more readily understood in conjunction with the drawings, inwhich:

FIG. 1 is a block diagram illustrating the functional components of drugpump devices in accordance with various embodiments;

FIG. 2 is a perspective view of a piston pump device in accordance withone embodiment;

FIGS. 3A and 3B illustrate, in isometric views, the assembly of a pistonpump device with a hydrogel-based electrolysis pump in accordance oneembodiment;

FIGS. 4A-4C are drawings of a piston pump device with aliquid-electrolyte-based electrolysis pump at various stages during drugdelivery, illustrating the location of an electrode pair relative to theelectrolyte level in the electrolysis chamber;

FIGS. 5A-5F are drawings of piston pump devices withliquid-electrolyte-based electrolysis pumps in accordance with variousembodiments, illustrating various electrode arrangements that ensurecontact of the electrodes with the electrolyte regardless of theorientation of the devices;

FIG. 6 is a schematic drawing of a piston pump device including agas-permeable separator in the electrolysis chamber in accordance withone embodiment;

FIGS. 7A and 7B are schematic isometric and side views, respectively, ofa piston pump device with a honeycomb electrode structure in accordancewith one embodiment;

FIG. 7C shows the honeycomb electrode structure of FIGS. 7A and 7B incross section;

FIG. 7D shows a membrane-sealed honeycomb electrode structure with agas-inhibiting surface coating in accordance with one embodiment;

FIG. 8D is a schematic drawing of a piston pump vial with an interiorsurface coating in accordance with one embodiment;

FIG. 9 is a schematic drawing of a magnetic-induction-based pistonvelocity sensor in accordance with one embodiment;

FIGS. 10A-10E are schematic drawings of piston position sensors inaccordance with various embodiments;

FIGS. 11A and 11B are side and perspective views, respectively, of adiaphragm drug pump device in accordance with one embodiment; and

FIGS. 12A-12C are side views of a diaphragm drug pump device with asecondary pump chamber in accordance with one embodiment.

DETAILED DESCRIPTION

FIG. 1 illustrates, in block diagram form, the components of a drug pumpdevice 100 in accordance with various embodiments of the presentinvention. In general, the pump device 100 includes a drug reservoir 102that interfaces with a pump 104 via a displaceable member 106. Thedisplaceable member 106 may be, for example, a piston, diaphragm,bladder, or plunger. In use, the drug reservoir 102 is filled withmedication in liquid form, and pressure generated by the pump 104 movesor expands the displaceable member 106 so as to push the liquid drug outof the reservoir 102. A cannula 108 connected to an outlet of the drugreservoir 102 conducts the liquid to an infusion set 109. The cannula108 may be made of substantially impermeable tubing, such asmedical-grade plastic. The infusion set 109 may include a catheter thatis fluidically connected to the cannula 108 and delivers the drug to asubcutaneous tissue region. A lancet and associated insertion mechanismmay be used to drive the catheter through the skin. Alternatively, theinfusion set 109 may include another type of drug-delivery vehicle,e.g., a sponge or other means facilitating drug absorption through theskin surface.

The pump 104 may utilize any suitable pumping mechanism such as, forexample, electrochemical, osmotic, electroosmotic, piezoelectric,thermopneumatic, electrostatic, pneumatic, electrohydrodynamic,magnetohydrodynamic, acoustic-streaming, ultrasonic, and/or electricallydriven (e.g., motorized) mechanical actuation. In certain embodiments,electrolysis provides the mechanism that mechanically drives drugdelivery. An electrolysis pump generally includes anelectrolyte-containing chamber (hereinafter also referred to as the“pump chamber”) and, disposed in the chamber, one or more pairs ofelectrodes that are driven by a direct-current power source to break theelectrolyte into gaseous products. Suitable electrolytes include waterand aqueous solutions of salts, acids, or alkali, as well as non-aqueousionic solutions. The electrolysis of water is summarized in thefollowing chemical reactions:

The net result of these reactions is the production of oxygen andhydrogen gas, which causes an overall volume expansion of the drugchamber contents. This gas evolution process proceeds even in apressurized environment (reportedly at pressures of up to 200 MPa). Asan alternative (or in addition) to water, ethanol may be used as anelectrolyte, resulting in the evolution of carbon dioxide and hydrogengas. Ethanol electrolysis is advantageous due to its greater efficiencyand, consequently, lower power consumption, compared with waterelectrolysis. Electrolysis pumps in accordance with several embodimentsare described in detail further below.

The pressure generated by the drug pump 104 may be regulated via a pumpdriver 110 by a system controller 112. For example, in an electrolyticpump, the controller 112 may set the drive current and thereby controlthe rate of electrolysis, which, in turn, determines the pressure. Inparticular, the amount of gas generated is proportional to the drivecurrent integrated over time, and can be calculated using Faraday's lawof electrolysis. For example, creating two hydrogen and one oxygenmolecule from water requires four electrons; thus, the amount (measuredin moles) of gas generated by electrolysis of water equals the totalelectrical charge (i.e., current times time), multiplied by a factor of¾ (because three molecules are generated per four electrons), divided byFaraday's constant. The volume of the gas can be determined, using theideal gas law, based on the pressure inside the pump chamber (and thetemperature). Accordingly, by monitoring the pressure inside the pumpchamber, it is possible to control the electrolysis current and durationso as to generate a desired volume of electrolysis gas, and therebydisplace the same volume of liquid drug from the reservoir 102.

In certain low-cost embodiments, the dose of drug to be delivered fromthe reservoir 102 is dialed into the device using a mechanical switch(e.g., a rotary switch), which then activates the pump 104, via thecontroller 112, to deliver the dose. In various alternative embodiments,the controller 112 executes a drug-delivery protocol programmed into thedevice or commands wirelessly transmitted to the device, as furtherdescribed below.

The system controller 112 may be responsive to one or more sensors thatmeasure an operational parameter of the drug pump device 100, such asthe pressure or flow rate in the drug reservoir 102 or cannula 108, thepressure inside the pump chamber, barometric pressure changes, or theposition of the displaceable member 106. For example, the controller 112may adjust the electrolysis based on the pressure inside the pumpchamber, as described above; due to the inexpensiveness of pressuresensors, this option is particularly advantageous for pumps designed forquick drug delivery. Two or more pressure sensors may be placed in thepump chamber to simultaneously monitor pressure therein, which providesadditional feedback to the controller 112, improves accuracy ofinformation, and serves as a backup in case of malfunction of one of thesensors.

In pump devices that are intended to operate over multiple days,typically in accordance with a non-uniform delivery protocol (e.g.,insulin delivery devices that are designed for 3-7 days of continuousdrug delivery), a flow sensor is preferably used to measure drug flowout of the cannula in real-time, and compute the total dose delivered byintegrating the flow rate over time. For safety, the device may include,in addition to the flow sensor, a pressure sensor inside the pumpchamber. This ensures that, in case the flow sensor fails, the pressuresensor would be able to detect high drug delivery rates, and shut thepump down to avoid administering an overdose to the patient. It alsoprovides extra safety by preventing chamber explosion at very highpressure when a failure mode occurs. Conversely, the combination of flowand pressure sensors can also detect a violation in the drug reservoir102 if pressure is measured in the pump chamber but no flow is measuredin the cannula 108, indicating a potential leak.

In general, the sensors used to measure various pump parameters may beflow, thermal, time of flight, pressure, or other sensors known in theart, and may be fabricated (at least in part) from parylene—abiocompatible, thin-film polymer. Multiple pressure sensors may be usedto detect a difference in pressure and calculate the flow rate based ona known laminar relationship. In the illustrated embodiment, a flowsensor 114 (e.g., a MEMS sensor) is disposed in the cannula 108 tomonitor drug flow to the infusion site, and detect potentialobstructions in the flow path, variations in drug-pump pressure, etc.The cannula 108 may further include a check valve 116 that preventsbackflow of liquid into the drug reservoir 112. Like the sensor 114, thecheck valve 116 may be made of parylene. In other embodiments, siliconor glass are used in part for the flow sensor 114 and valve 116construction. The drug pump device 100 may include electronic circuitry118 (which may, but need not, be integrated with the system controller112) for processing the sensor signal(s) and, optionally, providing pumpstatus information to a user by means of LEDs, other visual displays,vibrational signals, or audio signals. In addition to controlling thedrug pump 104, the controller 112 may be used to control othercomponents of the drug pump system; for example, it may triggerinsertion of the lancet and catheter.

The system controller 112 may be a microcontroller, i.e., an integratedcircuit including a processor core, memory (e.g., in the form of flashmemory, read-only memory (ROM), and/or random-access memory (RAM)), andinput/output ports. The memory may store firmware that directs operationof the drug pump device. In addition, the device may include read-writesystem memory 120. In certain alternative embodiments, the systemcontroller 112 is a general-purpose microprocessor that communicateswith the system memory 120. The system memory 120 (or memory that ispart of a microcontroller) may store a drug-delivery protocol in theform of instructions executable by the controller 112, which may beloaded into the memory at the time of manufacturing, or at a later timeby data transfer from a hard drive, flash drive, or other storagedevice, e.g., via a USB, Ethernet, or firewire port. In alternativeembodiments, the system controller 112 comprises analog circuitrydesigned to perform the intended function, e.g., to deliver the entirebolus upon manual activation by the patient.

The drug-delivery protocol may specify drug delivery times, durations,rates, and dosages, which generally depend on the particularapplication. For example, some applications require continuous infusionwhile others require intermittent drug delivery to the subcutaneouslayer. An insulin-delivery device may be programmed to provide a both acontinuous, low basal rate of insulin as well as bolus injections atspecified times during the day, typically following meals. To implementa dinner pump, for example, the instructions may cause the pump toadminister a 150 μL dose of insulin immediately after dinner, and todispense another 350 μL at a basal rate over eight hours while thepatient sleeps. In general, drug pump devices 100 may be configured toachieve sustained drug release over periods ranging from several hoursto several months, with dosage events occurring at specific times ortime intervals. Flow rates of fluid flowing through the cannula 108 mayrange from nanoliters per minute to microliters per minute. A clinicianmay alter the pump programming in system memory 120 if the patient'scondition changes.

Sensor feedback may be used in combination with a pre-programmeddrug-delivery protocol to monitor drug delivery and compensate forexternal influences that may affect the infusion rate despite unchangedelectrolysis (such as backpressure from the infusion site or cannulaclogging). For example, signals from the flow sensor 114 may beintegrated to determine when the proper dosage has been administered, atwhich time the system controller 112 terminates the operation of thepump 104 and, if appropriate, causes retraction of the delivery vehicle.The system controller 112 may also assess the flow through the cannula108 as reported by the flow sensor 114, and take corrective action ifthe flow rate deviates sufficiently from a programmed or expected rate.If the system controller 112 determines that a higher flow rate of drugis needed, it may increase the current to the electrolysis electrodes toaccelerate gas evolution in the electrolysis chamber; conversely, if thesystem controller 112 determines that a lower flow rate of drug isneeded, it may decrease the current to the electrolysis electrodes.

The pump driver 110, system controller 112, and electronic circuitry 118may be powered by a battery 122. Suitable batteries 122 includenon-rechargeable lithium batteries approximating the size of batteriesused in wristwatches, as well as rechargeable Li-ion, lithium polymer,thin-film (e.g., Li-PON), nickel-metal-hydride, and nickel cadmiumbatteries. Other devices for powering the drug pump device 100, such asa capacitor, solar cell or motion-generated energy systems, may be usedeither in place of the battery 122 or supplementing a smaller battery.This can be useful in cases where the patient needs to keep thedrug-delivery device 100 on for several days or more.

In certain embodiments, the drug pump device 100 includes, as part ofthe electronic circuitry 118 or as a separate component, a signalreceiver 124 (for uni-directional telemetry) or a transmitter/receiver124 (for bi-directional telemetry) that allows the device to becontrolled and/or re-programmed remotely by a wireless handheld device,such as a customized personal digital assistant (PDA) or a smartphone150. A smartphone is a mobile phone with advanced computing abilitythat, generally, facilitates bi-directional communication and datatransfer. Smartphones include, for example, iPhones™ (available fromApple Inc., Cupertino, Calif.), BlackBerries™ (available from RIM,Waterloo, Ontario, Canada), or any mobile phones equipped with theAndroid™ platform (available from Google Inc., Mountain View, Calif.).

The smartphone 150 may communicate with the drug pump device 100 using aconnection already built into the phone, such as a Wi-Fi, Bluetooth, ornear-field communication (NFC) connection. Alternatively, a smartphonedongle 152 may be used to customize the data-transfer protocol betweenthe smartphone and the drug pump device 100, which facilitatesoptimizing the sender and/or receiver components 122 of the drug pumpdevice 100, e.g., for reduced power consumption, and may provide a layerof security beyond that available through the smartphone. A smartphonedongle is a special hardware component, typically equipped with amicrocontroller, designed to mate with a corresponding connector on thesmartphone (e.g., a Mini USB connector or the proprietary iPhoneconnector). The connector may accommodate several power and signal lines(including, e.g., serial or parallel ports) to facilitate communicationbetween the dongle and the smartphone and to power the dongle via thephone.

In certain embodiments, the smartphone 150 and pump device 100communicate over a (uni- or bidirectional) infrared (IR) link, which mayutilize one or more inexpensive IR light-emitting diodes andphototransistors as transmitters and receivers, respectively. Datatransfer via the IR link may be based on a protocol with error detectionor error correction on the receiving end. A suitable protocol is theIrDA standard for IR data communication, which is well-established andeasy to implement. Communication between the drug pump device 100 andthe smartphone 150 may also occur at radio frequencies (RF), using,e.g., a copper antenna as the transmitter/receiver component 124. Thetransmitter/receiver 124 and associated circuitry, which maycollectively be referred to as the communication module of the drug pumpdevice 100, may be powered by the battery 122 and/or by the signaltransmitted from the smartphone 150 or other communication device. Insome embodiments, the communication module remains in a dormant stateuntil “woken up” by an external signal, thereby conserving power.

In some embodiments, the smartphone 150 is used to send real-timesignals to the drug pump device 100, for example, to turn the pump on oroff, or to adjust an otherwise constant drug delivery rate, and in someembodiments, the smartphone serves to program or re-program the drugpump device 100 for subsequent operation over a period of time inaccordance with a drug-delivery protocol. The communication link betweenthe smartphone and the drug pump device 100 may be unidirectional(typically allowing signals only to be sent from the phone and receivedby the drug pump device) or bi-directional (facilitating, e.g.,transmission of status information from the drug pump device 100 to besent to the smartphone). A special software application 154 (e.g., aniPhone “app”) executing as a running process on the smartphone 150 mayprovide a user interface for controlling the drug pump device 100 viathe smartphone display. As a security measure, the application 154 maybe configured to be accessible only when the dongle 152 is connected tothe smartphone 150. The application may further facilitate communicationbetween the smartphone 150 and a remote party. For example, ahealth-care provider may communicate with his patient's smartphone 150to obtain status updates from the drug pump device 100 and, based onthis information, push a new drug-delivery protocol onto the patient'ssmartphone, which in turn uploads this new protocol to the drug pumpdevice 100.

The functional components of drug pump devices as described above may bepackaged and configured in various ways. In certain preferredembodiments, the drug pump device may be integrated into a patchadherable to the patient's skin. Suitable adhesive patches are generallyfabricated from a flexible material that conforms to the contours of thepatient's body and attaches via an adhesive on the backside surface thatcontacts a patient's skin. The adhesive may be any material suitable andsafe for application to and removal from human skin. Many versions ofsuch adhesives are known in the art, although utilizing an adhesive withgel-like properties may afford a patient particularly advantageouscomfort and flexibility. The adhesive may be covered with a removablelayer to preclude premature adhesion prior to the intended application.As with commonly available bandages, the removable layer preferably doesnot reduce the adhesion properties of the adhesive when removed. In someembodiments, the drug pump device is of a shape and size suitable forimplantation. For example, certain pump devices in accordance herewithmay be used to deliver drug to a patient's eye or middle ear. Ophthalmicpump devices may be shaped so as to conform to the patient's eyeball,and may include a suitable patch for adhesion to the eyeball.

The various components of the drug pump device may be held within ahousing mounted on the skin patch. The device may either be fullyself-contained, or, if implemented as discrete, intercommunicatingmodules, reside within a spatial envelope that is wholly within (i.e.,which does not extend beyond in any direction) the perimeter of thepatch. The housing may provide mechanical integrity and protection ofthe components of the drug pump device 100, and prevent disruption ofthe pump's operation from changes in the external environment (such aspressure changes). The control system components 110, 112, 118, 120, 122may be mounted on a circuit board, which is desirably flexible and/ormay be an integral part of the pump housing. In some embodiments, theelectrodes are etched, printed, or otherwise deposited directly onto thecircuit board for cost-savings and ease of manufacturing.

The housing may contain the infusion set 109. Alternatively, theinfusion set 109 may be separately housed, mounted on a secondskin-adhesive patch, and tethered to the drug pump device 100 via thecannula 108. Such a tethered infusion set 109 may be advantageousbecause it generally provides greater flexibility for the placement andorientation of the insertion set 109 and drug pump device 100 son thepatient's skin. Further, it allows leaving the insertion set 109 inplace while removing the pump device 100, for example, for the purposeof replacing or refilling the drug reservoir 102.

In some embodiments, the drug reservoir 102 and pump 104 are stacked ina double-chamber configuration, in which the drug reservoir 102 isseparated from the pump chamber by a flexible diaphragm. Typically, thepump chamber is formed between the skin patch and the diaphragm, and thedrug reservoir 102 is disposed above the pump 104 and formed between thediaphragm and a dome-shaped portion of the housing. In alternativeembodiments, the drug pump device has a pen-injector configuration,i.e., the reservoir 102, a piston movable in the reservoir, and the pump104 driving the piston are arranged in series in an elongated (e.g.,substantially cylindrical) housing. A pump device with thisconfiguration may be integrated horizontally into a skin patch forprolonged drug infusion. Alternatively, it may be used as a handheldinjection device that is oriented substantially perpendicularly duringinjection, much like a conventional pen injector. Compared with theconventional injector that is mechanically activated by the patient, adigitally controlled electrolysis-based pump device as described hereinprovides the advantage of better dosage control. Various diaphragm pumpand piston pump configurations are described in more detail below.

The drug-delivery device 100 may be manually activated, e.g., toggled onand off, by means of a switch integrated into the pump housing. In someembodiments, using the toggle switch or another mechanical releasemechanism, the patient may cause a needle to pierce the enclosure of thedrug reservoir 102 (e.g., the septum of a drug vial) to establish afluidic connection between the reservoir 102 and the cannula 108;priming of the pump can then begin. Coupling insertion of the needleinto the reservoir 102 with the activation of the pump device ensuresthe integrity of the reservoir 102, and thus protects the drug, up tothe time when the drug is injected; this is particularly important forpre-filled drug pump devices. Similarly, the lancet and catheter may beinserted by manually releasing a mechanical insertion mechanism. In someembodiments, insertion of the lancet and catheter automatically triggerselectronic activation of a pump, e.g., by closing an electronic circuit.Alternatively, the pump and/or insertion set may be activated remotelyby wireless commands. Drug pump devices integrated into skin patches mayalso be configured to automatically turn on once the skin patch 102 isunwrapped and moisture is sensed. When drug delivery is complete, thedevice 100 may automatically retract the catheter and turn off the pump.

Drug pump devices 100 in accordance herewith may be designed for singleor repeated use. Multi-use pumps generally include a one-way check valveand a flow sensor, as described above, in the cannula. Further, the drugreservoir of a multi-use pump may be refillable via a refill port,using, e.g., a standard syringe. In some embodiments, the drug pumpdevice 100 is removed from the patient's skin for re-filling. Thepatient may, for example, place the drug pump device 100 and cartridgecontaining the new drug into a home refill system, where the pump deviceand cartridge may be aligned using, e.g., a press-machine mechanism. Thepatient may then press a button to trigger automatic insertion of aneedle that draws liquid drug from the cartridge to the cannula in orderto activate the electronics and begin priming the pump. In a furtherembodiment, a two-channel refill system may be used to aspirate old drugusing one channel as well as load new drug into the drug pump device 100using the other channel. One channel of the two-channel refill system isconfigured to regulate the flow and storage of drug, while the other oneis configured to regulate the flow and storage of waste liquid. Thesystem may use pneumatic pressure and/or vacuum control to direct theinfusion and suction of liquid in and out of the drug pump, and mayinclude sensors to monitor the pressures, and sterile filters to keepair from contaminating new drug. The drug pump device need notnecessarily be removed from the patient for refilling with thetwo-channel system, as the system may provide sufficient and flow andpressure control to prevent accidental drug infusion into the targetregion (e.g., by infusing liquid below the cracking pressure of a checkvalve).

In some embodiments, multiple drug pump devices are integrated into oneskin-adhesive patch. The devices may be arranged in an array on the samesurface, stacked on top of one another, or a combination of both. Theymay share the same insertion set, or, alternatively, each device mayhave its own insertion set and drug outlet. A multiple-outletarrangement facilitates administering several smaller doses over alarger surface area using multiple delivery vehicles, which may help toreduce systemic side effects (such as scarring and damage tosubcutaneous tissue) that results from drug deliver at highconcentrations to a small target area. In some embodiments, themulti-pump system includes, in addition to the drug reservoirs of theindividual devices, a shared reservoir. During operation of any one ofthe pump devices, drug may be expelled from the respective reservoirinto the shared reservoir, from where it is conducted to the infusionsite.

The volume of drug stored in the various pump devices may be the same orvaried, and may be as little as 50 μL or less. The pumps may functionseparately or collectively to deliver variable dosage volumes,essentially achieving controllable dosage resolution equal to an averagedosage delivered by each pump. Parallel operation of the pumps may leadto faster response times and better control over the overall flow rate.For example, if a high flow rate is desired, all of the pumps maysimultaneously be active. Further, the use of multiple, independentlyoperable pumps provides redundancy, should any of the pumps fail.

In some embodiments, the individual drug reservoirs store differentdrugs, facilitating variable drug mixing through selective pumpactivation. Different drugs may be administered together as part of adrug “cocktail” or separately at different times, depending on thetreatment regimen. Multiple reservoirs may also facilitate mixing ofagents. For example, one reservoir may store, as a first agent, a drugthat is in a “dormant” state with a half-life of several months, andanother reservoir may contain, as a second agent, a catalyst requiredfor activating the dormant drug. By controlling the amount of the secondagent that reacts with the first agent, the drug delivery device is ableto regulate the potency of the delivered dosage. The pumps may beoperated by a single controller, which may be programmed to deliver thevarious drugs in accordance with a user-selected drug-delivery protocol.As explained above, pump operation may be altered through wirelessreprogramming or control.

1. Piston Pump Devices

FIG. 2 shows an exemplary drug pump system 200 including a piston pumpdevice 202 and an associated tethered infusion set 204, both mounted toskin-adhesive patches 206. The pump device 202 includes a cylindrical(or, more generally, tubular) vial 208 with a piston 210 movablypositioned therein and an electrolysis electrode structure 212 mountedto one end. The structure 212 may be made of any suitable metal, suchas, for example, platinum, titanium, gold, or copper. In anotherembodiment, the structure 212 may include a support made from plastic orglass containing the electrodes inside a sealed pump chamber. The piston210 separates the interior of the vial 208 into a drug reservoir 214 anda pump chamber 216. A cannula 218 connects the drug reservoir 214 to theinfusion set 204. The piston pump device 202 is enclosed in a protectivehousing 220, e.g., made of a hard plastic.

The vial 208 may be fabricated from a glass, polymer, or other materialsthat are inert with respect to the stability of the drug and,preferably, biocompatible. Glass is commonly used in commerciallyavailable and FDA-approved drug vials and containers from many differentmanufacturers. As a result, there are well-established and approvedprocedures for aseptically filling and storing drugs in glasscontainers, which may accelerate the approval process for drug pumpdevices that protect the drug in a glass container, and avoid the needto rebuild a costly aseptic filling manufacturing line. Using glass forthe reservoir further allows the drug to be in contact with similarmaterials during shipping. Polymer vials, e.g., made of polypropylene orparylene, may be suitable for certain drugs that degrade faster when incontact with glass, such as protein drugs.

Suitable glass materials for the vial may be selected based on thechemical resistance and stability as well as the shatterproof propertiesof the material. For example, to reduce the risk of container breakage,type-II or type-III soda-lime glasses or type-I borosilicate materialsmay be used. To enhance chemical resistance and maintain the stabilityof enclosed drug preparations, the interior surface of the vial may havea specialized coatings. Examples of such coatings include chemicallybonded, invisible, ultrathin layers of silicone dioxide or medical-gradesilicone emulsions. In addition to protecting the chemical integrity ofthe enclosed drugs, coatings such as silicone emulsions may provide foreasier withdrawal of medication by lowering internal resistance andreducing the amount of pressure needed to drive the piston forward andexpel the drug.

In certain embodiments, the drug pump device is manufactured by fittinga conventional, commercially available glass or polymer drug vial, whichmay already be validated for aseptic filling, with the piston andelectrolysis pump, as shown in FIG. 3A. The piston 300 may be disposedinside the vial 302 near one end, leaving room for the electrolysis pump304, and a septum 306 may be disposed at the other end to seal the vial.Both the piston 300 and the septum 304 may be made of an elastomericpolymer material, such as a synthetic or natural rubber; in someembodiments, silicone rubber is used. A screw-in needle cassette 308 maybe placed over the septum 304, as illustrated in FIG. 3B, and amechanical actuation mechanism may serve to screw the cassette into thevial 302 such that the cassette needle punctures the septum 304 andestablishes a connection with the cannula at the time the patientdesires to use the pump. To accommodate the electrolysis pump 304, thevial 302 is, in some embodiments, longer than typical commerciallyavailable vials, but maintains all other properties such that validatedfilling methods and the parameters of existing aseptic filling linesneed not be changed. The drug pump device may be furnished with aprefilled vial. If a glass vial is used, the drugs can be stored in thepump device for long-term shelf life without the need to change thelabeling on the drug.

In applications involving dry-powder or lyophilized drug preparations,dual-compartment vials, also known as mix-o-vials, may be employed inthe drug pump device. These vials may incorporate a top compartmentcontaining a diluent solution and a bottom compartment containing apowdered or lyophilized drug. The two compartments may be separated by arubber stopper. Electrolysis may be used to actuate a mixing system thattriggers the piercing of the stopper to cause the top and bottomcontents to mix before or during infusion. For lyophilized and powdermedications, vials of borosilicate glass are particularly suitable. Thevial bottom may be specially designed to optimize cake formation andenhance the efficiency of the reconstitution process. Borosilicate vialsalso offer good hydrolytic resistance and small pH shifting, and are notprone to delamination. They are commercially available in both clear andamber varieties, with capacities ranging currently from 1.5 to 150 cm³.

FIG. 4A illustrates schematically a piston pump device 400 having aconventional electrolysis pump chamber 402 filled with liquidelectrolyte. As gaseous electrolysis products are generated, they pushthe piston 404 towards the outlet end of the drug reservoir 406 (seeFIG. 4B). Movement of the piston 404 increases the volume of theelectrolysis chamber 402, causing a decrease in the level of theelectrolyte 408. Depending on the orientation of the device, one or bothelectrodes 410 may, as a result, gradually emerge from the electrolyteand become surrounded by the gas, eventually forming an open circuit(FIG. 4C). This causes the electrolysis reaction to cease. Various drugpump embodiments that avoid this problem are described below.

In some embodiments, the electrodes are arranged such that at least aportion of each electrode remains submerged in electrolyte partiallyfilling the electrolysis chamber regardless of the device orientation.For example, as illustrated in FIG. 5A, electrode pairs 500, 502 may belocated on both ends of the electrolysis chamber 504, i.e., at or nearthe interface of the electrolysis chamber 504 with the piston 506 aswell as at the opposite wall 508 sealing the vial. The cathodes 500 andanodes 502 on either side of the electrolysis chamber 504 may beconnected by a flexible wire 506 of sufficient length to accommodateseparation of the two walls of the electrolysis chamber 504 aselectrolysis proceeds and the contents of the vial are expelled. Asillustrated by the five depicted device orientations at 0°, ±45°, and±90° with respect to a horizontal plane, this electrode arrangementensures at least partial submergence of the electrodes 500, 502 in theelectrolyte 510 regardless of orientation. Changes in orientation asdepicted arise, as a practical matter, from different patientorientations during sleep or activity, throughout which drug deliveryneeds to continue. FIG. 5B shows a modification of this electrodearrangement, in which the electrode pairs 520, 522 are angled relativeto the walls of the electrolysis chamber 504. In the example shown inFIG. 5C, multiple electrode pairs 530, 532 are positioned on each sideof the electrolysis chamber 504.

FIG. 5D shows an embodiment in which two parallel electrode spring coils540, 542 are utilized. These two coils 540, 542 may be supported by aseries of electrically isolating spacers 544 in a ladder-likeconfiguration that prevents short circuits between the two coils 540,542. This double coil set is compressed into the electrolysis chamber504 so that, as the piston moves forward, the coils extend to keep partof the coil pair submerged in electrolyte 510. This arrangement may bemodified by disposing multiple coil pairs 540, 542 in the electrolysischamber 504 to provide redundancy in case of a short circuit between thecoils of any coil pair. In yet another embodiment, illustrated in FIG.5E, a flexible parallel pair of wires 550, 552 separated by multiplespacers 544 in a ladder-like configuration is utilized. One end of thiswire pair 550, 552 is affixed to the piston 506, and the other end isattached to the opposing wall of the electrolysis chamber 504. As thepiston 506 moves, at least part of the wire pair 550, 552 will remainsubmerged in electrolyte for continuous and steady gas generation.

In another embodiment, illustrated in FIG. 5F, two pairs ofinterdigitated microelectrodes 560, 562 are used, one attached to thepiston 506 and the other one located at the opposite, fixed wall of theelectrolysis chamber 504. The cathodes 560 of the microelectrode sets onboth ends of the electrolysis chamber 504 may be connected with aflexible wire 564, as may the two opposed anodes 562. In thisarrangement, as in the previous examples, part of the electrode pair560, 562 will be submerged in electrolyte 510 to continuously produceelectrolysis gases irrespective of the orientation of the pump device.As will be evident to those skilled in the art, other electrode designsmay also be used to ensure immersion of at least a portion of anelectrode pair in the electrolyte.

In some embodiments, schematically illustrated in FIG. 6, agas-permeable separator 600 partitions the pump chamber 602 into anelectrolyte-filled compartment 604 at the back end and a gas compartment606 adjacent the piston 608. The gas-permeable separator 600 isgenerally impermeable to liquid electrolyte, but allows gaseouselectrolysis products to pass. Suitable separators are known to personsof skill in the art, and include, for example, thin silicone membranes,polymer membranes (e.g., made of polyurethane, carboxylated poly(vinylchloride), or parylene), microporous polymer films with polymericcoatings, or porous metal films. The separator 600 is fixedly mountedwithin the pump chamber 602; as a result, the electrolyte compartment604 has a constant volume. As an electrode pair 610 disposed in theelectrolyte compartment 604 breaks down liquid electrolyte into gasproducts, the gas penetrates the separator 600, entering the gascompartment 606 and driving the piston 608 forward; consequently, thevolume of the gas compartment 606 increases. Due to the large expansionratio associated with the phase transition from liquid electrolyte togaseous products, the volume of the gas compartment 606 generallyincreases orders of magnitude (e.g., hundreds- or thousandfold) fasterthan the volume of liquid electrolyte in the electrolyte compartment 604decreases. As a result, the electrodes 610 remain submerged in theelectrolyte throughout significant displacement distances of the piston608. The volume of the electrolyte compartment may be chosen, based onthe expansion ratio of the employed electrolyte and the initial drugreservoir volume, such that contact between the electrodes and theelectrolyte is ensured until the drug has been fully expelled.

Yet another approach involves absorbing the electrolyte within a matrixthat fills the interior of the pump chamber, or at least a portion ofthe chamber containing the electrodes. The matrix may be any absorbent,three-dimensionally networked material, for example, the solid phase ofa gel, cotton, a superabsorbent polymer, a sponge material, or anycombination thereof (such as, e.g., a gel absorbed within a sponge). Itsfunction is to maintain a persistent distribution of the electrolytethroughout the matrix, thereby ensuring that the electrodes, which areembedded in or filled with the matrix, remain in contact withelectrolyte.

Additional examples of suitable matrix materials include other fiberssuch as natural or synthetic cellulose based materials (e.g., rayon),acetate fiber, nylon fiber, hemp, bamboo fabric, wool, carbon basedfibrous material, silk, polyester, or other cotton-blend fibers.Ultra-fine cellulose nanofibers (with diameters of 1-50 nm), made using,for example, a combination of TEMPO, NaBr, and/or NaClO oxidation ofnatural cellulose (e.g., wood pulp), in different nanofibrous compositeformats include small diameter, high surface-to-volume ratio, easysurface functionality, good mechanical properties, and good chemicalresistance. Fibers with hydrophilic and water-absorbent properties tendto be preferable; they include “polymer molecules” that are linked up inrepetitive patterns or chains, negative charged materials that helpattract and absorb “dipolar” water molecules, and fibers with capillaryaction, where the fibers are able to draw or suck in water like a strawthrough the interior of the fiber. Capillary action is present both inthe fiber of the cotton plant and cotton fabric. Once drawn in throughthe fibers, the water is then stored in the interior cell walls.

A particularly advantageous matrix material is hydrogel, a highlywater-absorbent network of hydrophilic polymer chains. Hydrogels cancontain large fractions (e.g., more than 99% by weight) of water or anaqueous solution. They are highly biocompatible, and their absorbedliquid maintains most of its original liquid properties (e.g., density,phase change, and incompressibility), which makes the gels stable formechanical operation. Using hydrogel also facilitates easier packagingin low-cost manufacturing.

Electrolytes used with the hydrogel system may generally be aqueoussolutions, i.e., solutes dissolved in water. Examples of solutes includesalts (e.g., sodium chloride, magnesium sulfate, or sodium sulphate),dilute acids (e.g., sulfuric acid, hydrochloric acid, or amino acid),and dilute alkali (e.g., sodium hydroxide, potassium hydroxide, calciumhydroxide). Instead of water, other liquids, such as oil or ethanol, maybe used as solvents. Depending on the electrolyte used, the electrolysisgas includes a combination of hydrogen, oxygen, and/or carbon dioxide.For example, electrolysis of water results in oxygen and hydrogen gas,whereas electrolysis of ethanol results in carbon dioxide and hydrogengas. The use of ethanol may lower the power consumption of theelectrolysis pump and extend the life of the battery.

In some embodiments, the water contained in the hydrogel itself servesas the electrolyte. The volume expansion from liquid water to hydrogenand oxygen gas is more than a thousand times. Consequently, a pumpchamber volume of less than 1/1000 that of the drug reservoir may, atleast theoretically, suffice to expel all the drug from the reservoir.However, to increase the reliability of the electrolysis pump, a volumeratio such as 1 to 5 (electrolysis chamber to drug reservoir) may bepreferable. For example, for drug reservoir volumes of 0.5 mL, 3 mL, or5 mL, the corresponding volume of electrolysis chamber may be 0.1 mL,0.6 mL, or 1 mL, respectively. Still, use of an electrolysis pumppermits the size of the pump to be reduced significantly compared withconventional drug pumps, such as, e.g., motorized drug pump devices.

The matrix material may be placed next to electrodes in a single pumpchamber, or in multiple electrolysis cells (e.g., as described withrespect to FIGS. 7A-7D below). FIG. 3A shows a basic single-chamberconfiguration of a gel-based electrolysis pump, in which a pair ofelectrode poles breaks the electrolyte contained in the gel into gasbubbles (e.g., hydrogen bubbles and oxygen bubbles), which causeexpansion of the bubble-gel mixture. The expanding gel mechanicallycouples the pump chamber to the piston. In place of electrode poles,more complex electrode structures, such as planar interdigitatedelectrodes (as shown in FIG. 11B in the context of a diaphragm pumpdevice) may be used. In an alternative embodiment, a coaxial electrodepair having a pole-shaped core electrode arranged along the axis of atubular (e.g., cylindrical) sleeve electrode may be used.

In some embodiments, multiple coaxial electrode pairs, which arepreferably arranged in parallel in a close-packed pattern, are used tocompartmentalize the pump chamber into several electrolytic cells. Theindividual cells may be driven separately or in combination, whichfacilitates precise and smooth actuation of the piston. Operating thecells consecutively may contribute to maintaining contact between thehydrogel and the respective active electrode pair while gas is generatedover time. A multi-cell electrode structure also increases thereliability of the pump device due to redundancy: because of the largevolume expansion ratio, a single cell may be able to drive the pistonfrom the beginning to the end of drug delivery. In some embodiments, theelectrolysis cells are activated in a serial fashion, one after theother as electrolyte in the respective active cells dries out, toprolong the overall lifetime of the pump; cell activation may becontrolled by the electronic circuitry and based, for example, on ameasured electrolysis or flow rate.

FIGS. 7A and 7B illustrate drug pump embodiments that include multipleelectrolytic cells 700. Here, seven co-axial electrode pairs withhexagonal cross sections are arranged in a honeycomb structure 701,which is shown in front-view in FIG. 7C. The tubular sleeve electrodesmay (but need not) form a contiguous hexagonal latticework 702, and maybe manufactured from off-the-shelf metallic micro-honeycomb tubes.Typically (although not necessarily), the core electrodes 704 serve asthe anodes and the latticework 702 serves as the cathodes of therespective cells.

At the beginning of drug delivery from a filled reservoir 706, thehoneycomb electrode structure may extend through the drug pump chamber,from the back wall 708 of the chamber to the piston 710, as illustratedin FIG. 7B. As electrolysis gases are generated, the drug chamberexpands and the piston 710 moves towards the drug outlet. In someembodiments, the expanding gel 712 flows out of the tubular electrolysiscells 700 and enters the space between the cells 700 and the piston 710.In the alternative embodiment shown in FIG. 7D, the electrode cells 700are sealed by a porous membrane or other gas-permeable filter 714, whichmay be, as described above, a thin silicone membrane, a polymer membraneor a microporous polymer film. The filter 714 serves to retain the gel712 and electrolyte inside the electrolysis cells 700 while allowing gasto leave the cells 700 and fill and expand the space between the cellsand the piston 710.

In some embodiments, large portions of the interior surfaces of thehoneycomb electrodes 702 and portions of the core electrodes 704 arecoated with a material that inhibits gas formation, such as epoxy, whilesurface portions of the electrodes near the gas-permeable filter 714 areexposed (see FIG. 7D). For example, 10% or less of the electrode surfacearea may be uncoated. As a result of the coated and uncoated areas, gaswill be generated proximally to the filter 714, allowing hydrogel(and/or electrolyte) to be preserved inside the electrolytic cells 700for longer periods.

Some electrolysis pumps, such as smaller implantable pumps for drugdelivery to the eye or the middle ear, or refillable drug pumps (where adiaphragm or piston collapses back to its initial state after the drughas been refilled) desirably use a non-expanding fibrous material forthe matrix. Otherwise, expansion of the matrix could limit the collapseof the piston or diaphragm, and prevent the drug reservoir from beingfully refilled A non-expanding fibrous material can keep electrolytenear the electrodes, but does not interfere with the piston or diaphragmmotion.

Electrolysis pumps as described above generally facilitate continuouscontrol of the drug-delivery rate via the drive voltage or currentapplied to the electrodes. However, as the piston moves inside the drugvial, sudden changes in friction between the piston and the vial maycause the drug delivery rate to deviate from the intended deliveryprotocol, resulting, for example, in a non-uniform delivery rate despitea constant rate of electrolysis, or in undesired spikes in an otherwisesmooth uniform or non-uniform delivery protocol. Such changes infriction typically occur at the onset of piston movement as aconsequence of the difference between static and dynamic coefficients offriction: the static coefficient of friction between the piston and vialgenerally exceeds the dynamic coefficient of friction (usually by afactor of about two or three), so that the force needed to start thepiston in motion is greater than that needed to keep it moving. Inaddition, if the piston stops moving for a short period of time, alarger force is needed to re-initiate piston movement.

Furthermore, the dynamic friction itself may be affected by variationsin the surface properties of the piston and/or the vial along theirlengths, and/or by changes in the surface properties resulting from theinteraction between piston and vial. For example, if the inner diameterof the vial and/or the outer diameter of the piston vary slightly alongtheir lengths, the frictional forces generally depend on the pistonposition. Further, surface roughness may be smoothened out in time, inparticular, if a refillable drug pump device is used repeatedly.Conversely, discrete surface defects, e.g., a peck sticking out from theinterior surface of a glass vial, may roughen and/or damage the othersurface, e.g., the surface of a soft rubber piston. In general, thevariations in dynamic friction due to these and other effect are highlyunpredictable.

The difference between static and dynamic friction may be reduced byapplying a suitable surface coating to the interior surface of the vialand/or to the piston. In some embodiments, the vial (which may be made,e.g., of glass) is coated with a low-friction material such as, forexample, parylene or polytetrafluoroethylene (commonly known under thebrand name Teflon™), which reduces static friction without significantlychanging dynamic friction. Because vial surface coatings may be incontact with drugs or drug solutions, the coating materials arepreferably biocompatible to facilitate long-term drug stability. FIG. 8illustrates a drug vial 800 with an interior surface coating 802.

While the friction drop at the onset of piston movement can be mitigatedwith friction-reducing coatings, and variations in dynamic friction canbe minimized through high-precision manufacturing and selection ofsuitable combinations of piston and vial materials, in general theycannot be eliminated entirely. This problem may be addressed by usingpressure variations in the drug chamber to match the applied force tothe friction profile in order to maintain a desired piston velocity (orto change the piston velocity according to a desired protocol). For thispurpose, some drug pump embodiments include one or more sensors tocontinuously monitor a parameter indicative of or affecting drugdelivery. For example, a flow or pressure sensor placed inside thecannula may be used to measure the drug delivery rate directly, andfeedback circuitry can be employed to adjust the rate of electrolysis inresponse to sensed variations that deviate from the delivery protocol.

Alternatively, the movement of the piston may be monitored with aposition or velocity sensor. For example, in one embodiment, illustratedin FIG. 9, a magnet 900 is embedded in the piston 902, and an inductioncoil or coil sleeve 904 is wound around the drug vial such that, as themagnet 900 moves relative to the coil 904, an electric voltageproportional to the piston velocity is induced in the coil 904. To easemanufacturing, the piston 902 may be molded or otherwise manufactured toaccommodate the magnet 900 in a small pocket, allowing the magnet to bepress-fit into place in a simple assembly step. A lip may be included tohold the magnet in place. In yet another embodiment, the pressure insidethe pump chamber is measured continuously, allowing a sudden frictiondecrease or increase to be detected via a pressure drop or spike,respectively.

In response to the measured flow, pressure, position, or otherparameter, the system controller 112 may adjust the electrolysis rate inreal-time (or near real-time, e.g., within 1 ms of the friction change)to compensate for any variations in friction. Alternatively oradditionally, for changes in friction that are relatively predictable(such as the drop in friction at the onset of piston motion), thenecessary adjustments to the electrolysis may be determined empirically.For example, to avoid flow rate spikes as the piston begins to move, thetransition from static to dynamic friction may be repeated multipletimes while the electrolysis rate and piston position and/or flow ratein the cannula are measured simultaneously. From this data, theelectrolysis rate, as a function time, that is required to assure asmooth onset of piston motion may be calculated, and then programmedinto the pump device. The friction compensation techniques and featuresdescribed above apply similarly to a piston pump device that employs apump mechanism other than electrolysis, i.e., the pump rate may,generally, be controlled based on a measured drug delivery parameter toreduce or eliminate the effect of changes in friction on the drugdelivery rate.

When operating a drug pump device to inject liquid drug into a patient,it is often desirable to monitor the rate or volume of the injection orto track the filling status of the device, e.g., to alert the patient ofthe need to refill the device soon. This can be accomplished bymonitoring the position of the piston inside the vial. One approachutilizes the magnet 900 and one or more induction coils 904, as shown inFIG. 9. As the voltage induced due to the motion of the magnet 900relative to the coil 904 is proportional to the momentary velocity ofthe piston 902, integration of the voltage over time yields the pistonposition. Integrator circuits are well known in the art and can beimplemented without undue experimentation. This embodiment can be usefulwhen a simple, inexpensive pump is needed.

Rather than continuously monitoring the position of the piston, it oftensuffices to detect and signal certain threshold piston positionscorresponding to incremental amounts of drug remaining inside the vial,as depicted in FIGS. 10A-E. For example, an electronic display mayindicate when the drug reservoir is completely filled (corresponding toa piston position at the farthest possible distance from the drug outletto the cannula), 75% filled, 25% filled, or empty.

For example, FIG. 10A shows a low-cost embodiment in which the pistonposition is mechanically sensed with strings of different lengths. Thestrings 1000 may be tethered from the back wall or electronics end 1002of the drug pump chamber to the piston 1004. As the piston 1004 moves topush liquid out of the drug reservoir, the strings 1000 are stretcheduntil they break. Based on the ultimate tensile strengths of the stringmaterial, the lengths of the strings are chosen such that each stringruptures when the piston 1004 reaches a corresponding predeterminedposition. For example, the string that is intended to break when thedrug device is 75% filled has a length, immediately prior to breakage,that is the sum of the length of the drug chamber and a quarter of themaximum length of the drug reservoir. The strings 1000 may be, forexample, nylon strings or fine metal (e.g., copper or lead) wires. Ifthe vial and drug pump housing are transparent, string rupture may beobserved by eye. Alternatively, if the strings are electricallyconductive (as is the case with metal wires), their breakage may bedetected electronically. For example, the several wires of differentlengths may be part of respective electronic circuits, and their rupturemay cause a detectable open-circuit condition.

Position sensing may also be accomplished using multiple Hall effectsensors, optical sensors, induction coils, and/or capacitive sensorsplaced at different locations along the drug vial in combination with amagnet or optical component embedded in or attached to the piston;several embodiments are illustrated in FIGS. 10B-10D. For example, whena magnet 1010 associated with the piston 1004 passes a Hall effectsensor 1012 (FIG. 10B), the magnetic field strength detected by thesensor peaks, resulting in a voltage signal at that sensor. Similarly,as the magnet 1010 passes an induction coil 1014 (FIG. 10C), a voltagesignal is detected, enabling precise location of the piston. To detectthe piston motion optically, an LED may be attached to the piston andphototransistors may be placed alongside the vial to detect LED light asthe piston passes. Alternatively, as shown in FIG. 10D, the piston mayinclude a reflector 1016 (e.g., a piece of metal), and pairs of LEDs andphototransistor 1018 positioned along the vial may serve, respectively,to emit light and to measure the amount of reflected light, whichreaches a maximum when the reflector 1016 is closest to thephototransistor.

To detect the piston motion using capacitive sensing, one or multiplepairs of plate-electrodes 1020 are positioned along the length of thevial such that the piston 1004 moves between consecutive pairs ofplate-electrodes as the drug is dispensed. As the piston moves between apair of plate-electrodes, the dielectric medium between those particularplate-electrodes changes, thereby producing a detectable change incapacitance between the two plate-electrodes 1020. The piston 1004 maybe made from or contain material(s) that maximize the detectable changein capacitance, e.g., the piston may possess significantly differentdielectric properties than the drug in the vial.

Piston drug pump devices as described above may be manufactured fromvarious readily available components, and prefilled using existingfill/finish lines with few modifications. For example, as explainedabove, a conventional, FDA-approved drug glass vial may be used to housethe drug reservoir. A rubber stopper, optionally having a magnetattached thereto, may be placed into the vial to serve as the piston.The electrolysis chamber may be housed in a container that is open onone side so as to allow mechanical coupling between its contents and thepiston. A circuit board including the pump driver, system controller,memory, any other electronic circuitry, and battery (or other powersupply) may be attached to the back-end of the electrolysis chamber,which may be made of ceramics or plastics and include electricalfeedthroughs that allow electrical connections between the electrodesand the circuit board components. The circuit board may have the same ora similar diameter as the drug vial and pump, and may form, or beintegrated into, a cap that fits onto the pump. Alternatively, if thecircuit board is larger than the pump diameter, it may be placed to theside of the drug vial and pump assembly. The chamber may be filled withelectrolyte-absorbed hydrogel, and then fitted into (or onto) theback-end of the vial, thereby closing the vial.

The pump container may be made of glass. Its back-end may be sealed byheating it, e.g., in an oven or with a torch, and then crimping,twisting, or otherwise closing it, by hand or with a specially designedjig, while the glass is molten. The electrolysis electrodes may bepositioned and sealed in place as the glass is crimped. In someembodiments, the glass container holding the pump may be placed over aportion of the open drug vial like an end-cap. In other embodiments, theglass container is slid partially into the vial. Either way, theoverlapping wall portions of the vial and pump container may be bondedwith an adhesive sealant or through application of heat. In embodimentsthat utilize a honeycomb electrode or similar structure, this structuremay, itself, serve to contain the other drug pump components (such asthe hydrogel or other matrix material), and may be placed into the glassvial and secured, e.g., by a clamp-fit or screw mechanism. To preventleakage of the electrolyte out of the electrolyte chamber (which couldcause a short circuit in the circuit board), the electrolysis chambermay be sealed with a rubber O-ring.

Once the vial, piston, and pump are assembled, they may be sterilized,for example, by gamma-irradiation. One of the advantages of hydrogel andelectrolysis fluid is that they can readily be gamma-irradiated afterassembly. Sterilization serves to protect the patient from infection bypreventing bacteria and pyrogens from entering the final fluid pathwayof the device. The drug vial may initially be sterilized throughstandard techniques, for example, the use of heat or radiation. In oneembodiment, a metal barrier is placed over the septum beforesterilization of the vial (using, e.g., heat or radiation) to serve as abarrier during final sterilization steps using ethylene oxide or gases,preventing the gases from penetrating the septum.

Following assembly and sterilization of the vial, the vial may be filledwith liquid drug in a standard aseptic fill and finish line. For thatpurpose, the glass vial may be oriented vertically, with its back-end(where the piston is) at the bottom, and filled through the frontopening. After the filling step, the front-end of the vial is sealed,e.g., by placing a silicone septum in the opening and crimping a metalring cap to hold the septum in place. Finally, the vial assembly may beenclosed in an injection-molded protective housing, which may optionallyhave an adhesive on its underside. The housing may have separate frontand back portions (shown in FIG. 7B), which may be connected by aclip-mechanism. The front portion of the housing may include a needle topierce the drug vial's septum at time of use, and a cannula including aflow sensor and check valve for one-way flow.

Assembling the device (e.g., adding the pump chamber and outer casing),packaging the device in an outer sterile barrier, and boxing it forshipping may be performed with non-sterile techniques, before a finalsterilization is used to sterilize the rest of the pump (including theouter areas of the drug vial). This outer sterilization is particularlyimportant for any surfaces that are in contact with the drug.Post-sterilization processes such as treatment with ethylene-oxide gasor gas plasma, e-beam treatment, steam autoclaving, radiation treatment,chemical treatment, or dry heat treatment can all be used. In oneembodiment, the resulting drug device has a pump with a sterile drugvial that has an aluminum barrier over its pierceable silicone septum,and a loading needle that can be mechanically driven through the vial'sseptum and the metal barrier into the drug reservoir, whichsimultaneously activates the electronics and primes the pump.

Precisely controlled piston pump devices as described herein may beadvantageous over traditional body-adhered syringe systems, for example,because they can supply a larger overall volume of drug to a patientwhile reducing the flow rate from a rapid injection rate to a slowerrate of infusion over time. Due to the lower flow rate, a smaller needlemay be used to deliver the drug to the patient, resulting in less painto the patient. Further, in comparison with conventional, manuallyoperated pen injectors, electrolytically driven pump devices inaccordance herewith provide greater accuracy and precision in drugdosage, thus increasing patient safety and treatment efficacy.

2. Diaphragm Pump Devices

FIGS. 11A and 11B illustrate an exemplary diaphragm pump device 1100 incross-sectional and perspective views. The device 1100 contains, withina housing 1102 (which is partially removed in FIG. 11B for illustrativepurposes only), a drug reservoir 1104 and an electrolysis pump. The pumpincludes an electrolyte-filled pump chamber 1106 formed between a lowerportion of the housing 1100 and a diaphragm 1108. The reservoir 1104 islocated on the other side of the diaphragm 1108, above the electrolysischamber 1106, and is enclosed by the diaphragm 1108 and an upper,typically dome-shaped portion of the housing 1102. The reservoir 1104may include a refill port that allows for the introduction of additionaldrug. In some embodiments, the reservoir 1104 is capable of holdingbetween approximately one and ten mL of a drug and has an activeoperational lifetime of, e.g., between 30 minutes and 75 hours. Thecapacity and operational lifetime of the reservoir drug pump can easilybe adjusted by altering the size of the reservoir 1104 and the rate atwhich the drug is administered.

The drug reservoir 1104 opens into a cannula 1110, which conducts liquiddrug to an infusion set 1112 (not shown in FIG. 11A). The cannula 1110may contain a check valve 1113 to prevent blood or interstitial fluidfrom entering the reservoir 1104 and spoiling the drug, as well as aflow sensor 1114 for monitoring the rate at which drug flows to theinfusion set 1112. In some embodiments, the infusion set 1112 isdetachable from the drug pump device 1100, allowing the infusion set1112 to stay in place at the infusion site (e.g., with the cannulainserted into the patient's subcutaneous tissue) while the drug device1100 is removed for refilling or other purposes. Conversely, the pumpcan remain attached to the patient when the infusion needle or catheteris exchanged (which typically happens every few days). As illustrated inFIG. 11B, the drug pump device 1100 and infusion set 1112 may be mountedon two respective adhesive patches 1115 to be placed in contact with thepatient's skin.

A series of low-profile electrolysis electrodes 1116 are disposed at thebottom of the electrolysis chamber 1106. The pump control system may bedisposed below the electrodes 1116, e.g., embedded in the lower housingportion 1102. As shown in FIG. 11B, the electrodes 1116 may forminterdigitated comb-like structures—a configuration that is advantagesbecause it maximizes the opposing electrode surface area and minimizesthe distance between the opposing electrodes, resulting in high electricfield strengths in the interjacent space. The electrodes 1116 aregenerally made of a suitable metal, such as platinum, titanium, gold, orcopper, among others.

In operation, when current is supplied to the electrolysis electrodes1116, the electrolyte filling the pump chamber 1106 evolves gas 1120,expanding the diaphragm 1108 and moving it upwards, i.e., towards theupper portion of the housing 1102. As a result, liquid is displaced fromthe drug reservoir 1104 and forced into and through the cannula 1110 toa delivery vehicle that is part of the infusion set 1112. The diaphragm1108 may be corrugated or otherwise folded to permit a large degree ofexpansion without sacrificing volume within the drug reservoir 1104 whenthe diaphragm 1108 is relaxed. However, flat or bellows diaphragms mayalso be used. The diaphragm 1108 may be molded or microfabricated from,for example, parylene polymer. When the current is stopped, theelectrolyte gas 1120 condenses back into its liquid state, and thediaphragm 1108 recovers its space-efficient corrugations. Theelectrolysis pump may be smaller and more portable than other pumpsbecause of its lack of rigidly moving parts, and may be capable ofgenerating high pressures (e.g., greater than 20 psi), allowing the drugpump device to overcome any biofouling or blockages in the system.

The pump 1100 may include a magnet 1120 attached to the underside of thediaphragm 1108. As the magnet 1120 approaches the top of the drug dome1102, a sensor 1124 determines the relative distance between the magnetand the top of the drug dome, thus indicating when the pump is, e.g.,80%, 90% and 100% empty. The sensor 1124 may, for example, be a magneticinduction coil or a Hall effect sensor. In one embodiment, the pumpdevice alerts (e.g., by means of LED flashes and/or an audio alert, orby wirelessly signaling, for example, a smartphone) the patient when thepump is almost empty (e.g., 80% to 90% empty), and again when the pumpis completely empty.

FIGS. 12A-12C illustrate another embodiment of a diaphragm pump devicein accordance herewith. The device 1200 includes an electrolysis chamber1202, a secondary pump chamber 1204 adjacent the electrolysis chamber1202, and a drug reservoir 1206 disposed above the secondary pumpchamber 1204 and opening into a cannula 1208. The electrolysis chamber1202 and secondary pump chamber 1204 are connected via a fluid path thatmay be closed by a manually controlled pressure-release valve 1210. Thisvalve 1210 is closed when the electrolysis pump is active, allowing gasto evolve and pressure to build up inside the electrolysis chamber 1202,as shown in FIG. 12B. At least a portion of the enclosure of theelectrolysis chamber 1202—as illustrated, the corrugated diaphragm1212—has strong elastic properties. Therefore, when the electrolysispump is subsequently turned off and the valve to the secondary chamberis opened, recoil of the elastic enclosure 1212 forces fluid from thepressurized electrolysis chamber 1202 into the secondary pump chamber1204. As a result, a diaphragm 1214 separating the secondary pumpchamber 1204 from the drug reservoir 1206 expands, expelling drug fromthe reservoir 1206. A pressure sensor inside the electrolysis chamber1202 may be used to gauge when the electrolysis pump needs to be turnedon again. The pump device 1200 facilitates delivering drug continuouslywhile driving the electrolysis only intermittently, which may allowbuilding up a level of pressure inside the pump chamber greater thanthat achievable with sustained electrolysis. Consequently, this pumpconfiguration may be particularly useful for fast, high-pressure druginjections.

Mechanical recoil may similarly be exploited for power savings in a drugpump device that includes only a single pump chamber, but primary andsecondary drug reservoirs. The pump chamber and primary drug reservoirmay be arranged and function substantially like the pump device 1100shown in FIGS. 11A and 11B. Rather than conducting drug from the primaryreservoir directly to the infusion site, however, the drug is pumpedinto the secondary reservoir contained in a flexible bladder, whichresults in expansion and pressurization of the bladder. The electrolysispump may then be turned off, and the pressurized bladder thereuponslowly releases the drug for subcutaneous infusion.

Diaphragm pump devices in accordance herewith may include various pumpfeatures described above with respect to piston pump devices. Forexample, to ensure continuous contact between the electrolysis electrodestructure and the electrolyte despite changes in the orientation of thedevice, the electrolyte may be absorbed within a matrix material that isdisposed on top of, or otherwise placed in contact with, the electrodestructure. Preferably, the matrix material does not retain electrolysisgas and, therefore, substantially does not expand during electrolysis.This facilitates collapsing the expanded diaphragm to refill the drugreservoir to its original volume. In other embodiments, electrodestructures (such as a pair of spring coils or flexible wires) thatremain in contact with liquid electrolyte regardless of deviceorientation may be implemented in the electrolysis pump.

Having described certain embodiments of the invention, it will beapparent to those of ordinary skill in the art that other embodimentsincorporating the concepts disclosed herein may be used withoutdeparting from the spirit and scope of the invention. For example,various features described with respect to one particular device typeand configuration may be implemented in other types of device andalternative device configurations as well. Accordingly, the describedembodiments are to be considered in all respects as only illustrativeand not restrictive.

1. A drug pump device comprising: a vial comprising a drug reservoirtherein; a piston movably disposed inside the vial, a first side of thepiston facing the drug reservoir; a pump for applying pressure to asecond side of the piston so as to move the piston to cause drugdelivery from the reservoir; at least one sensor for measuring at leastone parameter indicative of a rate of drug delivery from the reservoir;and a controller responsive to the sensor for adjusting the pressure soas to compensate for variations in friction between the piston and aninterior surface of the vial.
 2. The device of claim 1, wherein thecontroller compensates for variations in friction due to a differencebetween a static coefficient of friction and a dynamic coefficient offriction between the piston and the interior surface of the vial.
 3. Thedevice of claim 2, wherein at least one of the vial or the pistoncomprises a surface coating that reduces the difference between thestatic coefficient of friction and the dynamic coefficient of frictionbetween the piston and the interior surface of the vial.
 4. The deviceof claim 3, wherein the surface coating reduces the static coefficientof friction between the piston and the interior surface of the vial. 5.The device of claim 3, wherein the surface coating comprisespolytetrafluoroethylene.
 6. The device of claim 3, wherein the surfacecoating comprises parylene.
 7. The device of claim 1, wherein thecontroller compensates for variations in friction due to a changingsurface property of at least one of the piston or the vial.
 8. Thedevice of claim 1, wherein the vial comprises at least one of glass or apolymer.
 9. The device of claim 1, wherein the vial is formed from aconventional drug vial.
 10. The device of claim 1, wherein the pump isan electrolysis pump.
 11. The device of claim 10, wherein the controlleradjusts the pressure by adjusting a rate of electrolysis.
 12. The deviceof claim 1, further comprising a cannula conducting liquid from the drugreservoir.
 13. The device of claim 12, wherein the at least one sensorcomprises a flow sensor positioned in the cannula.
 14. The device ofclaim 1, wherein the at least one sensor comprises at least one of apressure sensor or a barometric sensor.
 15. The device of claim 1,wherein the at least one sensor comprises a position sensor associatedwith the piston.
 16. The device of claim 15, wherein the position sensorcomprises a magnet associated with the piston and an induction coilsurrounding the vial.
 17. The device of claim 1, wherein the at leastone sensor comprises a pressure sensor and a flow sensor, inputs of thepressure and flow sensors facilitating recognizing malfunctions in thedevice.
 18. In a drug pump device comprising a drug reservoir and apiston, responsive to pressure, for forcing a fluid out of the drugreservoir, a method of compensating for variations in friction affectingmovement of the piston, the method comprising: measuring a parameterindicative of a rate of drug delivery from the reservoir; and based onthe measurement, adjusting pressure on the piston so as to compensatefor the variations in friction.